This invention relates to a device for the contactless measurement of the rotational speed of a first part which rotates during operation and is situated within a second part which either does not rotate or rotates at a rotational speed independent of the rotational speed of the first part.
The device is especially adequate for measuring the rotational speed, of a cylinder connected with the rotating turbine of an automatic transmission and is situated within a likewise rotating concentric pot, both parts being surrounded by a housing and the device having an arrangement that generates a magnetic field and a magnetic field detector.
Parts of an automatic transmission-like cylinders, which are connected with the turbine and, accordingly, rotate at the rotational speed of the turbine, are often located within other parts which are: either stationary or rotate at a rotational speed independent of the rotational speed of the turbine.
DE-A 36 20 884 has disclosed a device for detecting rotational speed and direction or rotation of a rotating part wherein the rotating part is, for example, a shaft or a rack with teeth formed of ferromagnetic material. A differential sensor of the magnetic field delivers input voltages for amplifiers on which band pass filters and comparators are mounted. By using rows of teeth, having identical spacings and gaps, there can be measured both the speed of movement and the direction of movement. Howeer, it is not possible with this known device to measure the rotational speed or direction of rotation of a rotating part which is surrounded by a second rotating or stationary part in which the measuring signal has to penetrate this second part.
EP-B 462 435 concerns an arrangement for detecting the rotational speed of a part rotating during, operation which has, in a peripheral direction, at least an unevenness with a rotational speed sensor device which detects the movement of the unevenness wherein a means generating a magnetic field and a magnetic field detector are combined to form a structural unit in which between the rotational speed sensor device and the rotating part, a wall is provided so that the rotational speed of the rotating part is detected through the wall. The magnetic field generator is a permanent magnet and the detector a magnetic field detector working according to the magnetic field principle. The rotational speed sensor is located in a bore of a housing of an automatic transmission of a motor vehicle which has an externally toothed first clutch bell housing and a second clutch bell housing situated between the rotational speed sensor and the first clutch bell housing. The magnetic field detector is especially sensitive in a direction determined by its shortest distance from the first clutch bell housing. In this manner, it is possible to detect through the rotating second clutch bell housing the change produced by the first clutch bell housing in the magnetic field generated by the permanent magnet. In this known arrangement, the basic material of the second clutch bell housing is demagnetized at least in sectors in peripheral direction in an area opposite to the magnetic field detector or is provided with a magnetization that generates a poled magnetic field. The magnetic field generator sits upon the rotating inner part while the magnetic field detector is situated within the housing.
The problem to be solved by this invention is, in a specially simple and reliable manner and without need of additional space, to measure the rotational speed of a rotating part situated within one other part which is either stationary or rotates at a second rotational speed independent of the first rotational speed, the first and the second parts being disposed concentrically to each other.
The inventive principle consists in providing as contactlessly working magnetic-field sensitive sensor a Hall-effect sensor with which the rotational speed of a rotating cylinder with integrated field spider is detected through a likewise rotating pot disposed concentrically thereto which is made from a non-magnetizable material. Since the field spider is entirely integrated in the first rotating part, i.e. the rotating cylinder, and since the Hall-effect sensor is integrated in the wall of the housing surrounding both parts, no additional space is required.
The inventive device is especially suitable for automatic transmissions of motor vehicles in which the first part is a cylinder firmly connected with the turbine and whose rotational speed is measured for regulation purposes.